1. Field of the Invention
The present invention pertains to the improvement of robustness in relation to multipaths of a dual-frequency receiver for satellite-based positioning.
2. Description of the Related Art
The measurements of pseudo-distances and of signal phases of a global navigation satellite system, or GNSS for “Global Navigation Satellite System” in English, for location and attitude measurement purposes, may be marred by large errors, if the propagation environment modifies the assumption of direct rectilinear trajectory between the satellites and the receiver.
This may, for example, be the case upon multiple reflections of the signals (multipaths) or upon maskings or obscurations (blade modulation in the case of installation on a helicopter).
Modern receivers generally integrate specific processing procedures, also called discriminators, for a correlation function so as to decrease the impact of the effects of the multipaths on the measurement of time received (by improving the code discriminator of the code tracking loops or DLL for “Delay Lock Loop” in English), but these processing procedures have a restricted domain of effectiveness (for example according to the delay of the paths) and entail only a small improvement in the carrier phase errors. Moreover, the extensions of the GPS system and the new GNSS systems base the monitoring of the integrity of the signals essentially on the coherence of the measurements of pseudo-distances and not on the measurements of the carrier phases.
Now, the phase of GNSS signals is increasingly becoming used for high-precision location (RTK for “Real Time Kinematic” in English) and attitude measurement applications with multiple antennas.
Known advanced schemes for reducing multipath errors in pseudo-distances, make use of the shape of the correlation function, such as the Double-Delta, MEDLL, or narrow-correlator schemes.
However, these schemes remain linked to propagation models (specular reflection, triangular correlation function, etc).